WDM Architecture Research Articles

Symmetric 10 Gbps PON Operating With a Single Laser Over 31 dB of ODN Loss

We propose a fully bidirectional and symmetrical 10 Gb/s on–off keying Passive Optical Network (PON) solution, using the same wavelength in both upstream and downstream directions. Thanks to the remodulation performed by the optical network unit, it is able to transport 20 Gb/s per wavelength using only one optical source for the full network, regardless of the number of users. The system is based on direct detection in downstream and self-coherent detection in upstream, over a standard of 31-dB loss splitter-based PON. We experimentally demonstrate the proposed architecture over a realistic PON fiber plant with one wavelength and commercial component. We then discuss the potential application of our solution in an ITU-T G.989 NG-PON2 point-to-point WDM architecture.

OFDM –WDM Architecture with Extended Reach and 1100 Split Ratio for Next Generation Passive Optical Networks

In this paper, we investigate OFDM-WDM-PON as an effective method for achieving high data rates in which OFDM is used as key element to combat dispersion. Large guard band intervals between adjacent OFDM symbols accommodate the distortion introduced by chromatic dispersion leading to reduced ISI. The system design involves the realization of FTTH by integrating OFDM, WDM and PON. OFDM also aids in improving receiver sensitivity. An aggregate of 40 Gbps, Direct detection OFDM-WDM-PON is designed and analyzed. Dispersion compensation techniques are used to achieve a bit error rate in the order of 10-8 and a split ratio of 1100 is achieved. Keywords: OFDM, PON, WDM

Minimizing Resource Protection in IP Over WDM Networks: Multi-layer Shared Backup Router [Invited

Optical networks and Internet Protocol/Multi-Protocol Label Switching (IP/MPLS) based networks have been traditionally designed and operated by separate departments of network operators. Likewise, both layers have always represented different business areas for system providers, which maintain different product lines for each of them. However, network operators have an IP/ MPLS over WDM architecture. The main drivers for this unique transport network are the cost savings achieved by simplifying the network infrastructure. Thanks to the advent of reconfigurable optical equipment and a multilayer control plane, 1 + 1 node protection at the IP layer in each location is no longer required. This work compares two resilience strategies on multi-layer network dimensioning: dual-plane protection and a multi-layer shared backup router (MLSBR). Based on the results of this paper, a MLSBR provides a significant reduction (up to 24%) on the required IP equipment in comparison with the IP protection approach.

Impact of channel-spacing on next 400 Gb/s Ethernet 40-km PMD based on [formula omitted] WDM architecture

The impact of fiber dispersion, system non-linearities and their interaction when varying the channel-spacing value, ranging from 200 to 800GHz, on the performance of a WDM 16×25Gb/s architecture that has been proposed as next 400Gb/s Ethernet (400GbE) 40-km physical medium dependent (PMD) sublayer is numerically analyzed. It is shown through calculations of the Quality Factor that the gain modulation nonlinearity of the semiconductor optical pre-amplifier is the main phenomenon that degrades the system performance. Moreover, it is demonstrated that its impact becomes dependent on the channel-spacing of the WDM plan, provided that the chromatic dispersion of the fiber is enough to vary the bit-correlation level among channels at the pre-amplifier input. Despite the considerable channel count, the effect of carrier heating-induced four wave mixing (FWM) is found to be rather modest, while the impact of carrier density pulsation-induced FWM and fiber non-linear response resulted to be negligible. With respect to the analyzed phenomena, a wide channel plan, only limited by the gain bandwidth, should be preferred for the 400 GbE implementation, especially if a nanostructured, broad-bandwidth, SOA can be afforded.

Total cost of ownership of WDM and switching architectures for next-generation 100Gb/s networks

The bandwidth efficiency and relative costs for 100 Gb/s WDM transport and switching architectures are compared in North American and pan-European long-haul networks. The first architecture uses muxponders and ROADMs for end-to-end wavelength transport with no digital sub-wavelength grooming. The other two utilize digital OTN switching, as either a standalone OTN switch or a converged integrated WDM/switch system, to efficiently groom services onto WDM wavelengths. Results show the integrated WDM/switch architecture utilizes the fewest WDM wavelengths and client service interfaces, and an integrated WDM/switch architecture using photonic integrated circuit technology provides the lowest operational costs.

GigaWaM—Next-Generation WDM-PON Enabling Gigabit Per-User Data Bandwidth

The “Gigabit access passive optical network using wavelength division multiplexing” project aims to implement 64-Gb/s data transmission over 20-km single-mode fiber. Per-user symmetric data rates of 1-Gb/s will be achieved using wavelength division multiplexing passive optical network (WDM-PON) architecture with a 1:64 user split per PON segment. Enabling technologies being developed within the scope of the project include tunable transceivers and athermal 50-GHz array waveguide grating multiplexer devices. The future-proof WDM architecture will enable convergence triple-play (telephony, TV, and broadband internet) service over existing optical infrastructure, and also facilitate cost-effective dense wavelength division multiplexing for metro aggregation and mobile backhaul networks.

Multilayer Traffic Engineering for IP Over WDM Networks Based on Bayesian Decision Theory

Network operators are migrating their networks to IP over WDM architectures. In such multilayer networks, it is necessary to define mechanisms that efficiently use the resources available from both layers in a coordinated manner. Thanks to the development of the control plane (GMPLS), it is feasible to both set up and tear down lightpaths automatically. Thus the WDM layer can now adapt its configuration to both meet a set of resource constraints and fulfill some predefined quality-of-service (QoS) requirements. To this end, we define a multilayer traffic engineering algorithm that efficiently manages the resources from both layers. This algorithm, which is based on Bayesian decision theory, finds the optimal number of label-switched paths that must be switched over the optical and electronic domains. Such an optimal value is found by trading off the QoS required by the users and the limited availability of network resources.

Experimental Investigation of Quality of Service in an IP All-Optical Network Adopting Wavelength Conversion

We experimentally show how the virtual private large-area network service (VPLS) technique, a layer 2 service, can improve optical network performance in terms of quality of service (QoS), and how a VPLS network behaves when it adopts all-optical wavelength conversion (AOWC), a new optical process that will be introduced in future optical networks. The advantages of VPLS are based on the capability to generate logical reliable paths in each wavelength channel, permitting suitable partitioning of the bandwidth according to the user requirements. In particular, we show the advantages of VPLS in access networks based on passive optical networks, and we test QoS properties of VPLS paths when an AOWC process occurs both in the core and in the access networks. The experimental investigation is carried out in a wide-area, all-optical gigabit Ethernet testbed with an access section based on an Ethernet passive optical network. As far as the core segment is concerned, we chose a high-efficiency AOWC process based on four-wave mixing in dispersion-shifted fiber; conversely in the access segment we chose a cheaper AOWC process based on cross gain modulation in a semiconductor optical amplifier. The reported results show that gigabit Ethernet transmission, with the relative layer 2 techniques, is also well suitable for wide-area WDM architectures, and in particular it is able to guarantee end-to-end QoS for huge bandwidth services such as high-definition TV and also in the case of congestion, restoration, and wavelength conversion processes.

Evaluation of IP over WDM Network Architectures

The commonly used IP-backbone network architecture of today is IP/ATM/SDH/WDM. This architecture has many redundant functionalities and is not optimized to transport IP traffic. New approaches for simplified network architectures try to eliminate redundant functionalities and to decrease the protocol overhead and thereby transport IP as efficiently as possible over WDM-based optical networks. EURESCOM project P918 “Integration of IP-over-optical networks: networking and management” investigated scenarios for optimized IP transport in WDM-based backbone networks. In this paper, three architectures, namely Gigabit Ethernet, Packet over Sonet/SDH and Dynamic Packet Transport are investigated and evaluated as an alternative to the IP/ATM/SDH/WDM architecture.

IP restoration vs. WDM protection: is there an optimal choice?

The exponentially growing number of Internet users armed with emerging multimedia Internet applications is continuously thirsty for more network capacity. Wavelength-division multiplexing networks that directly support IP-the so-called IP over WDM architecture-have the appropriate characteristics to quench this bandwidth thirst. As everyday life increasingly relies on telecommunication services, users become more and more demanding, and connection reliability is currently as critical as high capacity. Both IP and WDM layers can fulfil this need by providing various resilient schemes to protect users' traffic from disruptions due to network faults. This article first reviews the most common restoration and protection schemes available at the IP and WDM layers. These schemes may be present concurrently in the IP over WDM architecture, with the resilient mechanism of each connection specifically chosen as a function of the overall cost, application requirements, and management complexity. The article describes a versatile heuristic based on simulated annealing that may be adopted to optimize the concurrent use of IP restoration and WDM protection schemes in the same (mesh) network. The proposed heuristic allows varying the percentage of traffic protected by the WDM layer and that of traffic relying on IP restoration, taking into account topology constraints and network cost minimization. An additional feature of the proposed heuristic is the potential to trade solution optimality for computational time, thus yielding fast solutions in support of interactive design.

Steering of an optically driven true-time delay phased-array antenna based on a broad-band coherent WDM architecture

Performance of a six-channel (delay) three-antenna element coherent optically driven phased-array antenna which transports true-time delays from the controller to the antenna site over 4.4 km of single-mode fiber (SMF) are presented. We demonstrate accurate true-time delay and beam steering from 0.8-1.5 GHz. Wide bandwidth intermediate frequency (IF) filters are used to minimize the phase-to-intensity noise, resulting in a single-channel signal-to-noise ratio (SNR) and dynamic range of 49 (dB-MHz) and 94 (dB-Hz)/sup 2/3/, respectively. Additionally, using up-conversion at the antenna site, true-time delays at frequencies up to 18.3 GHz are demonstrated.

Calcite frequency splitter for dense WDM transmitter

An optical frequency splitter employing calcite crystals is demonstrated, to be inserted as a demultiplexer in a multimode transmitting stage for dense WDM architectures. The device operates on the optical state of polarization and is designed to separate four optical channels, /spl ap/39 GHz apart around /spl lambda/=1.5 μm. More than 28 dB of rejection between channels is achieved, while keeping overall losses level below 1 dB. Theoretical calculations and experimental results are presented.

Optical local area network technologies

To utilize the large bandwidth of optical fiber, optical LANs must employ architectures that fundamentally differ from current single-channel LAN architectures. With computer processor speeds continuing to grow exponentially and multimedia applications growing even faster, there is a strong need for higher-speed local area networks (LANs) that can handle the traffic generated by tomorrow's LAN users. Optical fiber is well suited for high-speed traffic transport, but the busty nature of computer traffic and large number of users makes it difficult to utilize the fiber's capacity in LANs. The incorporation of multiple payload channels in future LANs is seen as a necessity; WDM is a good candidate for achieving this. The rapidly improving optical component technologies allow more flexible WDM architecture designs for various emerging applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>